Move diff to core/diff

Signed-off-by: Derek McGowan <derek@mcg.dev>

core/diff/apply/apply_linux_test.go

@@ -0,0 +1,41 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package apply
+
+import (
+	"testing"
+)
+
+func TestGetOverlayPath(t *testing.T) {
+	good := []string{"upperdir=/test/upper", "lowerdir=/test/lower1:/test/lower2", "workdir=/test/work"}
+	path, parents, err := getOverlayPath(good)
+	if err != nil {
+		t.Fatalf("Get overlay path failed: %v", err)
+	}
+	if path != "/test/upper" {
+		t.Fatalf("Unexpected upperdir: %q", path)
+	}
+	if len(parents) != 2 || parents[0] != "/test/lower1" || parents[1] != "/test/lower2" {
+		t.Fatalf("Unexpected parents: %v", parents)
+	}
+
+	bad := []string{"lowerdir=/test/lower"}
+	_, _, err = getOverlayPath(bad)
+	if err == nil {
+		t.Fatalf("An error is expected")
+	}
+}